Having just watched The Hobbit: An Unexpected Journey for a second time I only just realised something; I don't know where the treasure in the troll-cave comes from.
I had assumed that as the trolls have traveled to their present location they were still on the move, and it doesn't look like the cave goes anywhere via a connected tunnel.
How did such treasures get to the cave?
I'm interested in the book and the movie, if possible then both.
The treasure in the Troll cave was gathered over time by waylaying travelers and by looting villages and farms. Ever hungry and always greedy, the Trolls collected anything they deemed of value from their victims and hoarded it in the cave they holed up in during daylight hours. It can be assumed that the trolls had other caves that they used along their route down from the mountains and would have brought their accumulated treasure with them when they moved on...
Regarding Glamdring and Orcrist, According to LOTR Wikia Elvish weapons from the First Age were taken as spoils of war and later used by Dwarves against Orcs in Battle of Nanduhirion
Years after the battle, the dwarven wielders of the Elvish swords were most likely relocating to Lindon during the Fell Winter of 2911 when they were waylaid unsuspectingly by trolls in the Ettenmoors. Thus the swords ultimately fell into the hands of the three trolls from The Hobbit by the end of the Third Age.
This is partially answered in the book itself, first of all in the initial description of the troll's lair:
There were bones on the floor and a nasty smell was in the air; but there was a good deal of food jumbled carelessly on shelves and on the ground, among an untidy litter of plunder, of all sorts from brass buttons to pots full of gold coins standing in a corner. There were lots of clothes, too, hanging on the walls-too small for trolls, I am afraid they belonged to victims - and among them were several swords of various makes, shapes, and sizes. Two caught their eyes particularly, because of their beautiful scabbards and jewelled hilts.
And secondly when Elrond examines the swords:
That day he looked at the swords they had brought from the trolls' lair, and he said: "These are not troll-make. They are old swords, very old swords of the High Elves of the West, my kin. They were made in Gondolin for the Goblin-wars. They must have come from a dragon's hoard or goblin plunder, for dragons and goblins destroyed that city many ages ago."
So while there is definitely a very large gap in the history of particularly the swords, it seems clear that much of the treasure was sourced from victims of the trolls, and supplemented by items somehow obtained from "a dragon's hoard or goblin plunder" (but Tolkien never states clearly how or when this happened).
"I could not say,"said Elrond, "but one may guess that your trolls had plundered other plunderers or come on the remnants of old robberies in some hold in the mountains. I have heard that there are still forgotten treasures of old to be found in the deserted caverns of the mines of Moria, since the dwarf and goblin war."
That is all that is said on the matter.
An alternate theory is that survivors of Gondolin fled the city carrying them, and eventually fled the destruction of Beleriand. Thus bringing them across the Misty Mountains. Perhaps they were slain by orcs or maybe even the ancestors of these trolls.
